1. Field of the Invention
The present invention relates to a high-aperture-ratio inner-focus telephoto lens used for example in single-lens reflex cameras and electronic still cameras, and more particularly to a high-aperture-ratio inner-focus telephoto lens having an angle of view equivalent to that of a lens with focal length of about 200 mm in case of 35 mm camera.
2. Related Background Art
A conventional high-aperture-ratio inner-focus telephoto lens is one having an angle of view equivalent to that of a lens with focal length of about 200 mm in case of 35 mm camera as disclosed for example in Japanese Laid-open Patent Application No. 53-134425, No. 59-116709 or No. 1-102413.
The lens as disclosed in Japanese Laid-open Patent Application No. 53-134425 has a big focusing lens group, which, in autofocus, forces a great load on a drive motor for the focusing group. Thus, the lens was disadvantageous in autofocus. Also, the lens as disclosed in Japanese Application No. 59-116709 has a focusing lens group composed of two groups which are moved at mutually different speeds, enabling compensation of aberration change in the near range. It had, however, drawbacks of complication and size increase of mechanism, because the focusing group was composed of the two groups. The lens as disclosed in Japanese Application No. 1-102413 has a nearest object distance of 2.5 m, which is relatively long among telephoto lenses having an angle of view equivalent to that of the lens with focal length of about 200 mm in case of 35 mm camera. Further, the imaging performance of the lens was not always satisfactory for shooting in the near range.